Microlithography is used for the production of microstructured components such as for example integrated circuits or LCDs. The microlithography process is carried out in what is referred to as a projection exposure apparatus having an illumination system and a projection objective. The image of a mask (=reticle) is illuminated via the illumination system and projected via the projection objective onto a substrate (for example a silicon wafer) which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection objective to transfer the mask structure onto the light-sensitive coating on the substrate.
Various approaches are known for specifically targetedly implementing adjustments or corrections with respect to polarization distribution in the illumination system or in the projection objective for optimizing the imaging contrast.
WO 2005/069081 A2 discloses, for example, a polarization-influencing optical element that includes an optically active crystal and a thickness profile which varies in the direction of the optical axis of the crystal.
It is known, for example, from US 2007/0146676 A1 to arrange in the illumination system a polarization manipulator for conversion of the polarization state, including a multiplicity of variable optical rotator elements by which the polarization direction of impinging linearly polarized light can be rotated with variably adjustable rotational angles.
WO 2005/031467 A2 discloses, for example, in a projection exposure apparatus, influencing the polarization distribution via one or more polarization manipulator devices which can also be arranged at a plurality of positions and which can be in the form of polarization-influencing optical elements which can be introduced into the beam path, where the effect of those polarization-influencing elements can be varied by altering the position, for example rotation, decentering or tilting of the elements.
U.S. Pat. No. 6,252,712 discloses, for example, a polarization compensator including two birefringent elements which are each provided with a free-form surface and which involve mutually rotated optical crystal axes.
It is known, for example, from U.S. Pat. No. 6,104,472 to use optical elements of quartz glass or calcium fluoride for controlling axial astigmatism, where the elements have mutually complementary aspheric surfaces and are arranged displaceably relative to each other with respect to their relative position.